Field of the Invention
The present application relates to a toner and a two-component developer that are used in electrophotography, image forming methods for visualizing electrostatic latent images, and toner jet.
Description of the Related Art
Japanese Patent Laid-Open No. 2000-75549 discloses that a graft copolymer of a polyolefin resin and a vinyl resin is added as an additive to a toner containing a polyester resin as a binding resin in order to improve the hot offset resistance of the toner. This technique enhances the dispersibility of the releasing agent, thereby improving the hot offset resistance of the toner. This technique has not, however, been examined under severe conditions as in the case of printing on both sides of thin paper having a basis weight of less than 70 g/m2. In order to reduce the occurrence of hot offset under such a condition, further improvement is desired.
Graft copolymers as used in the cited patent document can increase the dispersibility of the releasing agent, but tend to be compatible with the releasing agent. If the graft copolymer and the releasing agent are compatible with each other, they are plasticized to soften. This can degrade the durability of the toner in high-temperature environments.
Japanese Patent Laid-Open No. 2008-20848 discloses a toner containing a hybrid resin as a binding resin. The hybrid resin is produced by binding a polyester resin to a styrene-acrylic resin synthesized using an acrylic ester having a carbon number of 12 to 18 as a raw material monomer. This technique improves low-temperature fixability to some extent. In view of the fixability of the toner to thick paper having a basis weight of 100 g/m2 or more, however, further improvement is desired.
In addition, the acrylic ester unit, which has a low glass transition temperature (Tg), of the styrene-acrylic resin synthesized using an acrylic resin having a carbon number of 12 to 18 induces an external additive to be embedded in high-temperature environments, so that the durability of the toner is often unsatisfactory.
Japanese Patent Laid-Open No. 2013-24920 discloses an emulsion polymerized toner containing a block copolymer as a binding resin, produced by binding a styrene-based polymer block and a crystalline acrylate-based polymer block to a polyester skeleton. This block copolymer, which is a ternary block copolymer in which the polyester skeleton binds to the styrene-based copolymer block binding to the crystalline acrylate-based copolymer block improves the fixability and charging stability of the toner.
In a toner using such a binding resin, however, the dispersion of the releasing agent is liable to be insufficient. The fixability and hot offset resistance of such a toner are also desired to be improved. In addition, the styrene-based polymer block in the toner is compatible with the releasing agent. This makes the crystalline acrylate-based polymer block compatible with the releasing agent. Accordingly, the toner is unlikely to exhibit satisfactory durability if it is used in high-temperature environments.
As described above, there has been no development of a toner which can exhibit a high hot offset resistance even in the case of printing on both sides of thin paper, and also exhibit high durability in high-temperature environments, despite of demand for such a toner.